This invention involves radar signal processing. In particular, the present invention pertains to phase processing of received radar signals to reduce processing during range or target detection.
Radar systems have long been used to detect information about one or more target objects. The detected information may include, for instance, the position, direction of movement, velocity and/or acceleration of the target objects. Some radar systems transmit pulse or waveform signals having a fixed frequency. Other systems feature the use of waveforms with varying frequency, such as linear frequency modulated chirp pulses.
Radar systems can be categorized as being either a pulsed radar system or a continuous wave (CW) radar system, e.g. frequency modulated continuous wave (FMCW) radar system. Pulsed radars are fundamentally different from CW radars in several respects, including how the transmission signal is generated and varied over time. Both pulsed radars and FM-CW radars are described in Introduction to Radar Systems, 2nd Ed., McGraw-Hill 1986, Merrill Skolnik, which is incorporated by reference herein in its entirety.
Both pulsed radars and also FM-CW radars rely upon signal processing to detect the target object echo, sometimes called the return signal or reflection signal. Weak return signals and signals with high SNR are difficult to detect and often require complicated, computationally burdensome signal processing schemes.
Exemplary embodiments of the present invention are drawn to systems and methods for radar signal processing within a radar system to detect target objects. Signals are transmitted from a radar system according to predetermined frequencies having predefined transmission phase sequences. The return signals are from a target object and received back at the radar system. In accordance with the present invention, the transmit phase is removed from the homodyne-detected received return signal and the received signal having said transmit phase removed is analyzed to detect the presence of a return signal from the target object.
Exemplary embodiments of the present invention include performing an analog-to-digital conversion of the received signal, separating the received signal into quadrature I and Q components, and an initial low pass filtering the received signal. After the initial low pass filtering, exemplary embodiments of the present invention perform further low pass filtering by a second low pass filter acting on the received signal having said transmit phase removed. The step of removing the transmit phase from the received signal can be performed by multiplying a complex signal sequence of the received signal by a complex conjugate of the transmitted phase sequence. This can involve storing one cycle of the transmitted phase sequence for use in removing the transmit phase from the received signal, the length of the stored cycle of the transmitted phase sequence being determined by the relationship: 2xc2x7xcex94f/fm, wherein a variable xcex94f equals peak FM deviation and a variable fm equals a modulation rate.
In accordance with exemplary embodiments of the present invention, the received signal with its transmit phase removed can be applied to a number of range gates, each of which is matched to a delayed version of the transmitted signals from the radar system.